The invention generally relates to an insulated coil for coil and pole assemblies and to coiled frames. More particularly, the invention relates to a coil and pole assembly and a coiled frame which can be manufactured quickly with relative ease, and which has increased resistance to in-service environmental conditions.
Coil and pole assemblies normally include a magnetizing coil comprising a plurality of turns of copper wire or strap which surround a magnetizable ferrous metal pole. The several turns of the coil are electrically insulated from one another with a material or materials known as turn-to-turn insulation. In addition, the entire coil is electrically insulated from the pole with a material or materials known as ground insulation.
Conventional processes of providing turn-to-turn insulation and ground insulation are highly labor intensive. Presently, the manufacturing process typically comprises dipping the bare copper coil in a bake-dry varnish and then transporting the varnished coil to a turn-to-turn insulation station where sheets of insulation material are manually inserted between each turn of the coil. The coil is permitted to air dry for several hours to allow the varnish to penetrate or "wet" the sheets of insulation material. After the expiration of this time period, the coil is manually trimmed to remove the bulk of the sheet insulation material that extends beyond the periphery of each coil turn. Once having been trimmed, the coil is then pressed and cured. Typically, these steps are accomplished simultaneously by compressing the coil in a clamp fixture in both the horizontal and vertical directions within a hydraulic press and by attaching the coil leads to an electrical power supply that heats the coil. Once removed from the press, the clamped coil is permitted to cool. Upon removal from the fixture, remaining excess turn-to-turn insulation on the coil is removed, typically with the aid of a hand-held rotary brush.
After the turn-to-turn insulation has been applied in the manner described above, the coil is prepared for the application of ground insulation. Typically, the coil is moved to a ground insulation station where molding putty is applied to the ends of the coil and insulation tape wrapped about the coil. During the wrapping process, thermally resistant strips of material such as NOMEX.RTM. brand fiber products (NOMEX is a trademark of DuPont Co.), commonly referred to as shims, are added to the top and bottom surfaces of the coil to both ensure the correct coil height and to provide the arcuate surface necessary for proper attachment to a magnet frame. The insulation tape is carefully wrapped layer upon layer about the coil, inside and out, by hand. Armor tape is then wrapped about the insulation tape to provide a protective layer for the insulation tape.
At this point, the coil is prepared for assembly into the machine frame along with its associated pole. Once installed in the frame, power cables are attached to the coil leads, and the connections are hand-wrapped with insulation tape. After the coil and pole assemblies have been so installed, the coiled frame is varnish masked by hand and then preheated and vacuum pressure impregnated with varnish. The coiled frame is cured in an oven and permitted to cool. The coiled frame is then for a second time preheated, vacuum pressure impregnated with varnish, cured in an oven, and permitted to cool.
As can be appreciated from the above recitation, present manufacturing techniques used in insulated coil and coiled frame manufacture are time consuming and require a large amount of manual labor. In addition, such insulated coils are susceptible to mechanical failure and/or grounding due to compression and expansion of the coil during use, limiting the usable life of the coiled frame assembly.
From the above, it can be appreciated that it would be advantageous to have an insulated coil and coiled frame which avoids the problems identified above.